MED
In the literature: contested
Water exchange times across cell membranes in grey matter
In plain words
Water moves in and out of brain cells while it is being measured, which blurs the distinction between inside and outside. Reported exchange times disagree by large factors.
Precise statement
Determine the mean intra-to-extracellular water exchange time $\tau_{ex}$ in human and rodent grey matter, which reported analyses place anywhere from about 10 ms to over 100 ms, using diffusion-time-dependent kurtosis, filter-exchange imaging or multi-dimensional relaxation-diffusion methods, while separating exchange from structural time dependence. An answer is a value with uncertainty that is consistent across methods.
What would settle it
Agreement within 30 percent among independent exchange-sensitive methods on the same tissue, with a control of known permeability.